CN108028227B

CN108028227B - Surface mount device and method of attaching such a device

Info

Publication number: CN108028227B
Application number: CN201680039253.7A
Authority: CN
Inventors: S.诺伊延; R.尤巴赫斯; O.范德斯吕斯
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2015-07-02
Filing date: 2016-06-28
Publication date: 2021-11-30
Anticipated expiration: 2036-06-28
Also published as: US20180197835A1; WO2017001369A1; CN108028227A; EP3317896A1

Abstract

A device includes a surface mount component on a substrate, where the surface mount component is attached by a set of discrete mechanical coupling parts and by a bonding layer. This enables the mechanical coupling properties and the electrical/thermal properties to be optimized separately.

Description

Surface mount device and method of attaching such a device

Technical Field

The present invention relates to a surface mount device.

Background

The surface mount device is connected to the printed circuit board by solder interconnection or adhesive material. These materials are used for electrical, thermal (thermal) and mechanical purposes. In both die-attach and component-attach methods, the materials used are selected to meet stringent electrical and thermal requirements. Once a particular material meets these requirements, the mechanical reliability of the interconnect is optimized.

This optimization is a challenging task for both adhesive and solder materials. Most adhesive materials have low hardness and are mechanically compliant, but can only withstand limited thermal loads due to their low thermal conductivity. Most solder materials have a relatively high modulus, but suffer from low cycle fatigue (low cycle fatigue) when operated at typical service temperatures.

This indicates that there is a trade-off between the electrical, thermal and mechanical design of the interconnect. This trade-off prevents separate optimization of electrical, thermal and mechanical functions.

Disclosure of Invention

The invention is defined by the claims.

According to an example in accordance with an aspect of the present invention, there is provided a device comprising: a surface mount component and a substrate, wherein the surface mount component is attached to the substrate by a set of discrete mechanical coupling parts and by a bonding layer.

The mechanical coupling means are created by 3D printing on the substrate or 3D machining of the substrate and can separate the mechanical connection function from the electrical and thermal connection functions, which makes it possible to optimize these functions individually. The bonding layer may be designed to provide both electrical and thermal interconnects, or it may be specifically designed for its thermal characteristics. Separate electrical connections may then be provided.

The invention makes it possible to optimize thermal/electrical properties and mechanical lifetime separately, taking advantage of the specific benefits of separate materials, and no longer requires a trade-off between functionality and reliability.

The mechanical coupling means may for example comprise a planar interconnection, such as a bar (or post or slash), or an arrangement of bars, or a sheet structure lying in a plane.

The bonding layer may comprise a single connection area or it may have separate isolated portions. The bonding layer may be, for example, an electrically and thermally conductive adhesive layer. It can perform both electrical and thermal functions. The bonding layer may alternatively comprise one or more solder connections. There may be additional layers, such as solder connections forming a first bonding layer designed primarily for electrical connection performance, and adhesive layers forming a second bonding layer designed primarily for thermal coupling performance.

The mechanical components are optimized, for example, by creating a statically determinate fixation. This means that each degree of freedom of the surface mount device is uniquely limited. This avoids self-stresses on the structure due to, for example, thermal loads.

The mechanical coupling may be made at room temperature. Thus, the disadvantages of high temperature processing (e.g. exceeding the melting point of the material or high thermal stress) are eliminated. This makes its process compatible with any substrate, die or assembly, each substrate, die or assembly typically having the highest processing temperature.

The surface mount component for example comprises at least one electrical contact pad at the surface of the component base, which is connected to the substrate by a conductive adhesive layer. This base contact means that the connections between the surface mount component and the substrate need to be electrically conductive (unlike the case of surface mount components in which all connections are formed by leads extending laterally away from the device body). The electrical contact pads may be, for example, ground contacts.

The surface mount component may alternatively comprise a discrete component having a set of at least two contact terminals extending to the base surface. There may be, for example, contact terminals at opposite ends of the device connected down to the substrate. Alternatively, there may be an array of contact pads at the base of the surface mount component.

In another arrangement, a surface mount component includes a semiconductor component in which a semiconductor die is connected to a substrate by a conductive adhesive layer. This is used for the die attach process. In this case, the base of the surface mount component may not be a contact pad like this, but it may be a semiconductor layer.

In one example, the bonding layer may include an adhesive with embedded conductive particles. The use of solder can then be avoided by eliminating the need for strong mechanical coupling of the thermal and/or electrical connections. This in turn means that lower temperature processes can be used.

The bonding layer may alternatively comprise a solder connection or an array of solder connections, but with relaxed mechanical requirements.

Thus, the mechanical coupling component of the present invention may be used to (partially) replace the mechanical function of systems additionally using solder connections or systems with conductive adhesives. Thus, the inventive arrangement may be combined with solder or with a conductive adhesive. However, these connections no longer need to be designed to withstand mechanical loads.

One or more mechanical coupling components may be embedded in the bonding layer. For example, the bonding layer is applied after the mechanical coupling means have been formed.

Each mechanical coupling component may comprise one of:

a connecting rod, such as a strut or a slash;

a pair of intersecting connecting rods;

a pad defining a leaf spring;

defining patterned pads of the constrained leaf spring.

The design of the mechanical coupling components, their number, orientation and location are selected, for example, to provide a statically determinate coupling between the substrate and the surface mount component.

The substrate may include:

a semiconductor substrate; or

A printed circuit board; or

A lead frame; or

A flexible foil.

Thus, the present invention generally has broad applicability to surface mount technology.

The mechanical coupling component may be formed as an integral component with the substrate or directly on the substrate. This may be achieved, for example, by 3D machining of the substrate to define the mechanical coupling features in the top surface. Alternatively, the mechanical coupling components may be 3D printed on the top surface of the substrate, or the mechanical coupling components may be 3D printed on the top surface of the substrate by 3D printing the entire substrate or a portion of the substrate.

The mechanical coupling components do not necessarily play a role in the electrical and thermal interconnection between the assembly and the substrate.

The 3D printed component may instead be attached to the substrate using mechanical couplings, such as mechanical couplings that are themselves integrated with the substrate as part of existing (or future) substrate fabrication techniques. The coupling component may alternatively be manufactured separately, for example by moulding, die casting, machining or additive manufacturing (additive manufacturing) methods. They may be attached to the substrate by soldering, gluing, (3D) printing a connection layer such as solder, or by through-hole connection, for example using a snap-fit (snap-fit) connection.

The surface mount component may also have a snap-fit connection with the mechanical coupling part.

An example according to another aspect of the invention provides a method of making a device comprising:

mounting the surface mount component to the substrate using a set of discrete mechanical coupling components; and

the surface mount component is attached to the substrate using the bonding layer.

The bonding layer may again comprise a conductive adhesive.

The method may include forming the mechanical coupling component as an integral component with the substrate or directly on the substrate. The surface mount component may be assembled to the mechanical coupling component using a snap-fit coupling. The method may alternatively comprise forming the mechanical coupling component as an integral component of the surface mount component.

Drawings

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

fig. 1 shows a known surface mount device attached to a substrate;

FIG. 2 shows a first example of a surface mount device attached to a substrate;

FIG. 3 shows a second example of a surface mount device attached to a substrate;

fig. 4 shows three possible designs of mechanical coupling parts;

FIG. 5 shows four different coupling arrangements;

FIG. 6 shows a snap-fit coupling arrangement; and

fig. 7 illustrates a method of fabrication.

Detailed Description

The present invention provides a device comprising a surface mount component on a substrate, wherein the surface mount component is attached by a set of discrete mechanical coupling parts and by a bonding layer, such as a conductive adhesive layer, or a solder portion. This enables the mechanical coupling properties and the electrical/thermal properties to be optimized separately.

Fig. 1 shows a conventional surface mount device 10 connected to a substrate 12 using a solder or adhesive layer 14 that performs the interconnect function. It must meet electrical, thermal and mechanical requirements.

Figure 2 shows an example of the arrangement of the present invention. The interconnect function is shared between the two components. The first mechanical coupling part 20 provides a mechanical coupling. The second component 22 is a soft bonding material layer that meets thermal and electrical requirements, but need not provide a strong mechanical coupling.

Alternatively, there may be three components: mechanical coupling components 20, electrical connections such as solder connections or wire connections (which need not be designed to provide complete mechanical or thermal support), and adhesive layers that provide primarily thermal functionality.

The present invention is of particular interest for surface mount technologies that require conductive coupling between the body of the surface mount device and the underlying substrate, i.e., when the base of the surface mount device includes an area to which electrical contact is required.

This applies to semiconductor devices on semiconductor dies, where the die needs to be electrically connected to a controlled potential in order to avoid floating potentials. Thus, the electrical connections may not be connected to contact pads like this, but may be connected to the semiconductor die (in a die attach surface mounting process).

This also applies to electrical components (which may be active or passive) having contact terminals at their base. For example, a surface mount capacitor may have terminals at the ends that extend down to the underlying layer.

This also applies to electronic assemblies having a ground terminal at their base in addition to other terminals that may be provided by contact leads, for example.

This also applies to electronic assemblies having a set of contact terminals at their base, and these terminals may be the only contact terminals of the assembly.

In some other embodiments, the components may have the required electrical connections achieved by connecting wires or leads, or by solder ball connections such as ball grid arrays. In this case, the remaining thermal and mechanical functions can be decoupled by using mechanical coupling components and therefore no electrically conductive bonding layer. The present invention, however, is of particular interest for surface mount devices without leads.

The above example shows that the conductive adhesive layer may be a single layer as shown in fig. 2, but it may have

different portions

22a, 22b as shown in fig. 3 for electrical connection to different areas of the base of the surface mount component.

The separated

portions

22a, 22b may be separate areas of the conductive adhesive layer. Alternatively, the

portions

22a, 22b may be solder portions, which solder portions thus define the bonding layer. They provide thermal as well as electrical coupling. They also provide mechanical coupling, but may be relaxed in mechanical performance due to the use of mechanical coupling component 20.

In addition to the solder connection and the mechanical coupling means, a separate additional adhesive layer may optionally be provided. The additional adhesive layer may for example extend over an area larger than the area of the solder portion.

The connection between the component and the substrate may be considered to be a die attach component (which is used for thermal and mechanical coupling of the component to the substrate) and a component attach component (which is used for electrical coupling of the component to the substrate). The mechanical coupling components are used only as die attach components and they are designed to provide the required mechanical coupling properties.

The mechanical coupling component 20 secures the surface mount device 10 to the substrate with a mechanical connection that may be somewhat resilient. The connection is preferably statically determinate or approximately statically determinate.

The statically determinate structure (also called "equalization") is fully constrained and acts as a precisely constrained kinematic coupling. The structure reduces or eliminates the possibility of self-stresses (i.e., stresses without external loading) that may be caused by mechanical or thermal effects. Thus, the mechanical coupling can minimize internal load interaction between the component 10 and the substrate 12 and eliminate the possibility of self-stress.

In addition, the mechanical coupling may be designed to be stressed only in the elastic range. The coupling member in this way has only a reversible elastic deformation, so that after release of the current load, the mechanical coupling returns to its original shape. This reduces or eliminates fatigue in the coupled components, which increases the life of the components and system.

Stresses in the mechanical coupling and in the components themselves can be minimized, which maximizes lifetime.

The bonding layer may serve as both a thermal coupling and an electrical attachment for the component. Both functions may be performed by a single design of the bonding layer, such as a thermally conductive adhesive, or may be performed as separate components, such as an electrical solder joint bonded to a thermally coupled bonding layer.

The electrical and thermal functionality may be achieved using standard materials (e.g., standard high conductivity low hardness materials). One example is an adhesive filled with conductive particles. The mechanical properties of these materials are of secondary importance, since the mechanical functionality is achieved by the mechanical coupling component 20.

The invention therefore relates in particular to a mechanical coupling part 20 which enables an elastic (approximately) statically determinate fixing of the assembly 10 to the substrate 12.

Advances in additive manufacturing techniques (e.g., 3D printing) have enabled the fabrication of small, delicate resilient components such as leaf springs, constrained leaf springs, and slashes or struts (generally referred to herein and in the claims below as connecting rods).

Fig. 4 (a) shows the diagonal connecting strut 30 (referred to as a slash). Such a post may also be used as a vertical or horizontal connector. Fig. 4 (b) shows the leaf spring 32, and fig. 4 (c) shows one restricted leaf spring 34. The constrained leaf spring is patterned in its surface to define channels. These change the characteristics of the spring. The channel allows the top and bottom edges of the leaf spring to rotate relative to each other. Note that a pair of cross struts function in the same manner as a constrained leaf spring.

These structures are each planar (although the intersecting struts may have thicker central portions), and they allow some elastic deformation perpendicular to the plane.

Fig. 5 shows various possible connection schemes that provide statically determinate structure.

Fig. 5 (a) shows a set of three vertical couplings and a set of three lateral couplings between two components. The mechanical coupling components are all connecting rod couplings.

Fig. 5 (b) shows a set of two vertical couplings between two components, one of which includes the constrained leaf spring 34 and the other of which includes the full leaf spring. They are vertical, but orthogonal to each other. The complete leaf spring extends across the entire width of one side of the member so that only two mechanical coupling members are required to form the desired statically determinate structure.

Fig. 5 (c) shows a set of three vertical couplings between the two assemblies, each in the form of a pair of cross bars 30.

Fig. 5 (d) shows a set of three vertical couplings between the two assemblies, each in the form of a constrained leaf spring 34.

The number of mechanical coupling parts is independent of the number of electrical connections between the assembly and the substrate. For example there may be exactly two or three mechanical coupling parts, one of which is considered to comprise all parts attached to a specific location of the assembly, as shown in the above examples. For example, fig. 5 (a) shows three mechanical coupling components; one at each of the three corners of the assembly. Figure 5 (b) shows two mechanical coupling parts, one along one edge of the assembly and the other at the other corner.

The mechanical coupling component may be conductive or insulating. They are connected to regions of the component remote from (i.e. not including) the electrical contact terminals, for example the insulating regions of the component.

The height of the mechanical coupling part is designed such that the assembly is only loaded in the elastic range. As described above, the mechanical coupling component may be created, for example, by 3D printing on the substrate or 3D machining of the substrate itself, separate fabrication and subsequent attachment to the substrate or component, or by other methods.

The connection between the surface mount component 10 and the mechanical coupling element 20 may be made by a clip or a latching (clicking) system. Fig. 6 shows one possible solution.

The surface mount component 10 is snap-fitted in a retention channel 40 formed as part of the mechanical coupling part 20.

The invention may be applied to any surface mount device or die that needs to be attached to a substrate, such as a printed circuit board, a flexible foil, or a lead frame.

The mechanical coupling parts may for example be formed using metal such as aluminium or copper, but it is also possible to use plastic parts if for example injection moulding or 3D printing is used.

The mechanical coupling parts may have dimensions of a height of 10-300 μm and a width in the same range, e.g. the same height and width. The thickness of the component may be about 1-10 μm. Thus, the mechanical coupling component is a planar structure, which means that the thickness is at most 1/10 of the largest in-plane dimension, and the shape is generally flat, but not necessarily perfectly planar. In the case of struts as shown in fig. 4 (a), they are also planar in that the thickness is at most 1/10 of the length (which is the largest in-plane dimension). The struts may be considered one-dimensional links and the leaf spring or cross strut arrangement may be considered two-dimensional links.

Fig. 7 illustrates a method of fabrication.

Fig. 7 (a) shows a substrate 12, which may be a semiconductor substrate, a printed circuit board, a lead frame, or a flexible foil.

The mechanical coupling component 20 is formed, for example, by layer deposition (e.g., by a 3D printing process) over a substrate to provide the structure shown in fig. 7 (b).

As shown in fig. 7 (c), the surface mount component is attached to the mechanical coupling part 20, for example by a snap-fit coupling.

As shown in fig. 7 (d), and then an adhesive layer is injected. Alternatively, the adhesive layer may be applied prior to attaching the surface mount component 10 and then cured after attaching the surface mount component 10.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.

Claims

1. A surface mount device comprising:

a surface mount component (10);

a substrate (12);

a set of discrete mechanical coupling components (20; 30; 32; 34) and a bonding layer, which together bond the surface mount component (10) to the substrate,

wherein the surface mount component (10) and the mechanical coupling part (20; 30; 32; 34) are connected by a clip or a latching system such that the surface mount component (10) is snap-fit coupled to the mechanical coupling part, the mechanical coupling part (20; 30; 32; 34) being formed as an integral component with the substrate or directly on the substrate to provide a statically stable coupling between the substrate and the surface mount component by the clip or latching system, and wherein the bonding layer provides an electrical and/or thermal interconnection between the surface mount component and the substrate.

2. A device as claimed in claim 1, wherein the bonding layer (22) is a conductive adhesive layer.

3. A device as claimed in claim 2, wherein the bonding layer (22) comprises an adhesive with embedded conductive particles.

4. A device as claimed in claim 2 or 3, wherein the surface mount component (10) comprises at least one electrical contact pad at the base surface of the component, the at least one electrical contact pad being connected to the substrate by a layer of conductive adhesive (22).

5. A device as claimed in claim 4, wherein the surface mount component (10) comprises a ground contact at its base.

6. A device according to claim 4, wherein the surface mount component (10) comprises a discrete component having a set of at least two contact terminals extending to a surface of the base.

7. A device according to any of claims 1-3, wherein the surface mount component (10) comprises a semiconductor component, wherein the semiconductor die is connected to the substrate by a bonding layer (22).

8. A device according to any of claims 1-3, wherein one or more of said mechanical coupling parts (20; 30; 32; 34) are embedded in a bonding layer.

9. The device of any of claims 1-3, wherein each of the mechanical coupling components comprises one of:

a connecting rod (30);

a pair (32) of intersecting connecting rods;

a pad defining a leaf spring;

a patterned pad (34) defining a constrained leaf spring.

10. The device of any of claims 1-3, wherein the substrate (12) comprises:

a semiconductor substrate; or

A printed circuit board; or

A lead frame; or

A flexible foil.

11. A method of making a device, comprising:

mounting the surface mount component (10) to a substrate using a set of discrete mechanical coupling parts (20; 30; 32; 34) located between the surface mount component and the substrate, wherein the surface mount component (10) and the mechanical coupling parts (20; 30; 32; 34) are connected by a clip or a latching system such that the surface mount component (10) is snap-fit coupled to the mechanical coupling parts, the mechanical coupling parts (20; 30; 32; 34) being formed as an integral component with the substrate or directly on the substrate to provide a statically stable coupling between the substrate and the surface mount component by the clip or latching system; and

after mounting the surface mount component to the substrate, a bonding layer (22) is provided to bond the surface mount component to the substrate to provide electrical and/or thermal interconnection between the surface mount component and the substrate.

12. The method of claim 11, wherein providing a bonding layer comprises providing a conductive adhesive layer (22).